Fundamental fiber technologies have developed as the number of applications based upon light transmission through optical fiber has grown over time. In particular, developing techniques and devices for efficiently coupling light from optical sources into optical fibers as well as for coupling light from optical fibers to optical receivers has received considerable attention during this period of growth. The light beam emitted from the optical source, such as a diode laser, typically reaches the optical fiber at varying angles, depending on the light's initial angles of emission. This can result in some light beams failing to reach the fiber core or reaching the fiber core at an angle wider than the acceptance angle. Thus, these beams fail to become harnessed as light that propagates through the optical fiber for use in a given application. In particular, when light from the optical fiber is coupled to the optical receiver, such as a photodetector, if the receiver is not positioned with both its center aligned with the axis of the fiber and its face perpendicular to the fiber axis, the receiver may not capture the beam from the fiber. This inefficient coupling of light from the source to the fiber or from fiber to detector has a negative impact on the optical fiber application. In addition, another source of coupling inefficiency results from the difficulty in creating an optical coupling device with a working distance suitable for precisely focusing the incident light beams upon the fiber core or focusing the light from the fiber to the optical detector. These coupling inefficiencies have a direct impact on fiber optic telecommunications systems. For example, when less light reaches the fiber core, as a result of coupling inefficiencies for example, the signal transmission distance over which the light based signal can travel will be reduced as a result of the initial coupling inefficiency.
Various approaches have been developed to improve the coupling of the light source to the optical fiber or from the optical fiber to the optical receiver. Some of the approaches of the prior art are illustrated in FIGS. 1A-1E. FIG. 1A illustrates the light from an optical fiber 20 being directed to a photodetector 10 by an angled reflector 30. FIGS. 1B and 1C illustrate the light from an optical fiber 20 being directed to a photodetector 10 by the specially shaped fiber. FIG. 1D illustrates a system as shown in FIG. 1A with the addition of a lens 35 to focus the incident light 15 from a light source 10 upon the fiber core 25 at a known working distance or the light from the fiber 20 to the photodetector 10 at a known working distance. FIG. 1E illustrates a system incorporating a lensed optical fiber 40 with a spherical portion for directing the light 15 from a light source incident on the lensed fiber 40 into another optical fiber 20 or suitable for directing the light 15 from the fiber 20 to an optical receiver (not shown).
The devices shown in FIGS. 1A, 1B and 1C have the sole function of redirecting the light from optical fiber 20 along another optical path. In particular, the prior art devices shown operate solely by receiving the light 15 and bending the light 15 by an angle of approximately 90 degrees in order to send the beam in the direction of the photodetector 10. These three devices do not control the beam spot size or focus the beam at a prescribed working distance. Although the device shown in FIG. 1D can function, in principle, to control the beam spot and working distance, it entails troublesome alignment between the semiconductor laser or photodetector, lens, and optical fiber, and requires a coupling system of a substantial size. The lenses used in these devices are often bulky and occupy sufficient space such that the external lens based device cannot be used when coupling between an optical source array and an optical fiber array or an optical fiber array and detector array, in which a plurality of optical sources, or photodetectors, or optical fibers are arranged at short intervals. The device shown in FIG. 1E can also control the beam spot diameter and the working distance to an extent. However, the range of radii for the spherical portion of the lensed fiber is limited. This results in the range of possible spot sizes and working distances being accordingly limited. In addition, the spherical lensed fiber structure is complicated and difficult to make. Furthermore, it is difficult to focus a light spot with a diameter which is close to or less than the mode field diameter of a single mode fiber to an optical receiver or couple a light source with a spot diameter close to or less than the mode field diameter of a single mode fiber to a single mode fiber by using the devices illustrated in FIGS. 1D and 1E.
A need therefore exists for an optical coupling device and fabrication methods which result in an easily manufactured device that mitigates the problems of efficiently directing light from an optical source into an optical fiber or from an optical fiber to an optical receiver.